1. Field of the Invention
The present invention relates to an optical sensor using a light guide member.
2. Description of the Related Art
Lee A. Danisch, “Bend-enhanced fiber optic sensor”, SPIE vol. 1795 Fiber Optic and Laser Sensors X (1992) pp. 204-214 discloses a curvature sensor using an optical fiber. In this curvature sensor, a curvature detection portion is provided in part of the optical fiber. The optical fiber is constituted of a core and a clad, and the curvature detection portion is formed by damaging part of the clad. In light that is guided through the optical fiber, light that has reached the curvature detection portion is scattered by the curvature detection portion, and part of this light is radiated to the outside of the optical fiber. An amount of this light that is radiated to the outside varies in accordance with an amount and a direction of a curvature of the optical fiber. Therefore, measuring a light guide loss of the optical fiber can obtain an amount of curvature of the optical fiber.
Jpn. Pat. Appln. KOKAI Publication No. 2007-44412 discloses a curvature sensor that can detect curvatures at positions. This curvature sensor includes a light supply fiber and detection fibers. The detection fibers are arranged around the light supply fiber. Both an end of the light supply fiber and an end of each detection fiber are covered with a single mirror, and light exiting the light supply fiber is reflected by the mirror and enters each detection fiber.
Each curvature detection portion is formed in each detection fiber. The two detection fibers form one pair. The curvature detection portions are provided in the detection fibers at positions that are different from each other along a longitudinal direction in accordance with each pair. Although the curvature detection portions of the two detection fibers in the same pair are placed at the same position in the longitudinal direction, their positions around a center axis are different from each other. Therefore, in this curvature sensor, measuring a light guide loss of each detection optical fiber enables obtaining an amount of curvature and a direction of curvature at each of positions.
In the curvature sensor in Jpn. Pat. Appln. KOKAI Publication No. 2007-44412, the light exiting the a light supply fiber must be preferably distributed to the detection fibers, but the preferred distribution of the light is not described in Jpn. Pat. Appln. KOKAI Publication No. 2007-44412 at all. Specifically, this literature just gives a description that the light exiting the light supply fiber is reflected by the mirror and enters the detection fibers. As described above, in the configuration that an end of the light supply fiber and an end of each detection fiber are covered with the single mirror, the preferred distribution of the light cannot be expected.